During photosynthesis, unused oxygen atoms form oxygen gas (O2) that is released as a waste product. How did these oxygen atoms originally enter the plant? A. They were part of the ATP molecules gathered by the chloroplasts.
B. They were part of the sugar molecules (C6H12O6) the plant brought in for food.
C. They were part of the carbon dioxide (CO2) molecules that entered through the leaves.
D. They were part of the water molecules (H2O) pulled in through the roots.